Previous work has demonstrated that pts with chest pain and hypertrophic cardiomyopathy (HCM), or chest pain and normal coronary arteries, may have impaired vasodilator reserve compared to normal individuals. In order to determine if pts with chest pain and nonobstructive hypertrophic cardiomyopathy, who have previously been shown to have impaired vasodilator reserve, differ from individuals with nonobstructive hypertrophic cardiomyopathy who do not have chest pain, we compared myocardial metabolism and coronary vascular hemodynamics in 8 asymptomatic HCM pts with 26 nonobstructive HCM pts with chest pain. Great cardiac vein (GCV) flow, regional coronary vascular resistance, myocardial oxygen consumption and lactate extraction were measured at rest and after pacing at 150 bpm. Compared to symptomatic HCM pts, asymptomatic HCM pts had a greater increase in GCV flow and fall in coronary vascular resistance, for similar increases in myocardial oxygen demand with pacing. More symptomatic HCM pts (42%) had evidence of ischemia and produced lactate with pacing compared to asymptomatic HCM pts (14%). Thus, ischemia and angina in HCM appears to be due, at least partly, to impaired vasodilator reserve, but some asymptomatic HCM pts may also have ischemia which is silent.